A development of long term evolution (LTE) brings opportunities to both mobile carriers and device original equipment manufacturers (OEMs). Owing to an increased network capacity and throughput, many new technologies have been emerged. For example, a voice over LTE (VoLTE) technique transmitting voice calls through an LTE network provides salient advantages such as higher efficiency and global roaming. A VoLTE call may provide higher performance metrics than a legacy circuit switching (CS) call and a voice over internet protocol (VoIP) call. However, the reliability of the VoLTE call still lags behind that of the CS call and the VoIP call. Specifically, a call failure ratio including setup failures and unintended drop situations is almost 5 times higher than that of legacy calls (e.g., CS call and VoIP call). Such issues severely impair user experience. Therefore, diagnostic data needs to be collected to facilitate troubleshooting.